Vehicle windshield wiper systems typically include a drive motor that continuously rotates a crank arm. In order to translate the continuous rotation of the crank arm into the back and forth sweeping action needed in a wiper, a linkage connects the crank arm to the wiper. The linkage, usually a four bar linkage, has a main drive link that drives another arm connected to the wiper post. The wiper is oscillated back and forth between inner and outer wipe limits determined by the lengths of the various arms and links of the linkage, often with a large mechanical advantage. If obstructions such as ice and snow block the wiper from reaching the design limits, the linkage can see high tension or compression loads, high enough to strain the system. Some systems therefore incorporate a snow clutch located somewhere in the linkage, often between the crank arm and main drive link. Known snow clutches incorporate a member, such as a coil spring or block of elastomer, that can slip or give at high loads. Others use a pair of toothed disks loaded together by spring washers that can slip past one another at high loads. Besides the obvious cost and space disadvantages involved in providing the extra components needed, an inherent problem exists with any snow clutch that uses a yielding member like a spring. A spring yields in a continuous, linear fashion, proportional to the load. Yielding at lower, normal operating loads would change the link lengths and wipe pattern when it was not desired to to so. Therefore, the springs used in such designs are typically very large and heavy, so as to yield only at very high, excessive loads.